The present invention relates to a piezoelectric acoustic device, and more particularly to a piezoelectric acoustic device in the form of a piezoelectric speaker, a piezoelectric buzzer, or the like, for use in electronic equipment such as portable telephones or the like.
A number of piezoelectric acoustic devices are known for use in electronic equipment including, for example, the piezoelectric acoustic devices disclosed in Japanese Utility Model Publication No. 879/1984, Japanese Patent Application Laid-Open Publication No. 75578/1994, Japanese Patent Application Laid-Open Publication No. 28167/1995, U.S. Pat. No. 3,970,879, U.S. Pat. No. 4,122,365 and U.S. Pat. No. 4,183,017. Such prior art piezoelectric acoustic devices generally include a piezoelectric vibrator formed from a piezoelectric ceramic element and a receiving casing for receiving the piezoelectric vibrator. A portion of the receiving casing called a side wall is spaced apart from the piezoelectric vibrator to form a front air chamber. The receiving casing of a typical prior art piezoelectric acoustic device generally includes a centrally mounted cylinder disposed opposite the piezoelectric vibrator for communicating the sound generated by the piezoelectric vibrator in the front air chamber through the interior of a housing of an electronic device such as a portable telephone. When such a piezoelectric acoustic device is mounted in the housing of a portable telephone or other type of electronic device, a force or pressure is often exerted against the cylinder in the direction of the front air chamber. Also, when a waterproof or dust-proof cloth member is arranged between the housing and the cylinder, the cloth member exerts force or pressure on the cylinder in the direction of the front air chamber. When the force exerted against the side wall is high, or the mechanical strength of the side wall is low, the side wall may become deflected, resulting in a variation in the volume of the front air chamber, which can lead to variations in the sound produced by such piezoelectric acoustic devices. In order to solve this problem, it has been proposed to increase the thickness of the side wall to increase its mechanical strength. Unfortunately, such an approach results in an increase in the size of the piezoelectric acoustic device which is highly undesired in the art.